Tapetal Cell Wall Research Articles

THE CYTOLOGY OF POLLEN ABORTION IN C‐CYTOPLASMIC MALE‐STERILE CORN ANTHERS

Anther development of the C‐cytoplasmic male‐sterile (cms C) and the normal cytoplasm version (N) in the W182BN corn inbred was studied by light and electron microscopy. Deviation from normal pollen development was first observed in the tapetal cells at the tetrad stage of development. Two types of tapetal abnormalities were observed in plants with C cytoplasm. The first behaved like the N anther until the tetrad stage, when numerous small vacuoles appeared in the tapetal cells. Inner and radial tapetal cell walls broke down normally, but irregular Ubisch body deposition was observed, and exine development was inhibited and delayed. The tapetum and microspores disintegrated at the intermediate microspore stage. The second type of tapetum was highly vacuolated at the early tetrad stage, with dense inner and radial cell walls that remained intact and enlarged when the tetrads aborted. No organellar abnormalities, such as the mitochondrial changes observed in cms T, were observed in C anthers.

The causes of genetic male sterility in 3 soybaen lines

The cause of male sterility in 3 soybean lines, TGM 103-1, N-69-2774 and TGM 242-4 was studied. In TGM 103-1, which was both male and female sterile, two different abnormalities were associated with sterility. Precocious movement of a few chromosomes at the metaphase I stage resulted into the production of non-functional pollen while cells which underwent apparent normal meiotic division had disintergration of the tapetal cell wall immediately after the free microspore stage leading to the starvation and subsequent death of the developing microspores. In lines N-69-2774 and TGM 242-4, both of which were partially sterile, male sterility resulted from a failure of cytokinesis after the telophase II stage. Meiosis proceeded normally but the 4 microspores after telophase II failed to separate into pollen grains and degenerated thereafter.

Characterization of fibrous compound of Golgi vesicles in tapetal cells ofDelphinium

It was shown that Golgi structures abundantly appearing in tapetal cells ofDelphinium Ajacis L. developing anthers, prior to meiocytes meiosis, show a fine fibrous material within their vesicles. At the time of the formation of tapetal cell wall this fibrous component, released by an exocytotic process, is incorporated into the cell wall. The membrane of dictyosomes derived vesicles participates in the development of plasma membrane. Fibrous material appears to be morphologically similar to the fibrils of tapetal cell wall; this cell wall gives a positive reaction for cellulose and pectins, as visible in the light microscope. Moreover, the fibrous and pectinase resistant compound of dictyosomes derived vesicles and the fibrils of cell wall disappear partly after cellulase digestion which proves their cellulosic character. On the other hand pectinase treatment as well as ruthenium red staining suggest associated with cellulose pectins within Golgi vesicles.

Studies on Histological Features of Male Sterility in Sunflower (Helianthus annuus L.)

In order to clarify the morphological and physiological causality responsible for the sterility in sunflower, the authors carried out histological observations on the male sterile plants as comparing with fertile ones. Fertile and male sterile inflorescences of sunflower (Helianthus annuus L.) 'P 21 ms' which inherit male sterility genetically, were used for this study. For histological observations, paraffin sections were cut to a thickness 15 μm and stained with the modifications of triple stain of Himes'es et al.. On observation with the behavior of tapetum during microsporogenesis, the sunflower studied in this experiment belong to the plasmodial type. After the microspore stage, distinguishable differences in the anther were observed. The tapetal cell wall of the fertile anther breaks down, and the tapetal protoplasm extruds into the anther loculus to envelop the microspores. On the contrary, tapetal cell wall of the sterile anther exists in situ and the tapetal cell increase in size. In addition, at both sites and shapes of tapetal nuclei at the microspore stage, a clear difference between the two types of fertilities could be distinguishable. As a result it is concluded that the abnormality of the tapetal cell lysis is closely related with male sterility. And it is also presumed that the sites or shapes of the nuclei were related with male sterilty. For the histochemical reactions, no conspicuous difference between the types of fertilities could be observed.

THE EFFECT OF TEMPERATURE ON MEIOSIS AND POLLEN DEVELOPMENT IN WHEAT AND RYE

The durations of meiosis and pollen development were estimated in Petkus Spring rye and Chinese Spring wheat grown at 15, 20 and 25 °C. Over the range 15-25 °C, meiotic duration and pollen maturation time decreased with increasing temperature and the ratio between the durations of these stages at 25 °C and at 15 °C (Q10) indicated that the temperature responses of meiotic and pollen development were similar in both species. Both within and between species meiosis and pollen maturation had constant relative durations at each temperature. The effect of low temperature on the duration of meiosis and pollen development was similar in Holdfast, an extreme type of winter wheat, as in Chinese Spring. The relevance of these results to hybrid cereal breeding are mentioned. In plants grown at 25 °C, abnormal meiotic and pollen development resulting in male sterility was seen in some anthers. The cause of male sterility appeared to be thickening of tapetal cell walls concurrent with abnormal late meiotic development in PMC's.

A histochemical and ultrastructural study of the ontogeny and differentiation of pollen inPodocarpus macrophyllus D. Don

Male cones ofPodocarpus macrophyllus D. Don enter a period of dormancy lasting almost a year after the differentiation of archesporial tissue. The cell walls of the sporogenous and tapetal cells are different in composition from those of the cells comprising the wall of the microsporangium. The walls of tapetal cells undergo complete dissolution but the naked protoplasts do not invade the cavity of the microsporangium, and eventually degeneratein situ. Sporopollenin-containing bodies are formed on the tapetal plasmalemma although no specific tapetal organelles can be singled out as sites of synthesis of sporopollenin precursors. The original walls of the microspore mother cells are broken down completely and replaced by a thin callose-like wall. No cytomictic channels are formed prior to or during early meiosis. The outer nuclear membrane of the sporogenous cells forms numerous vesicles which likely play an important role in preparing the cell for meiosis and in the breakdown of the original sporogenous cell wall and the formation of the new wall. Pronounced evaginations and invaginations of the nuclear envelope during the tetrad stage are seen which again indicate vital nucleo-cytoplasmic exchange at the time when species specific sexine layer is being laid down. The microspore protoplast synthesizes a portion of sporopollenin precursors. Sexine and part of nexine I are laid down during the tetrad stage on lamellae of unit membrane dimensions while nexines II and III are formed after the dissolution of the tetrads by the coalescence of small, electron dense particles. Cells of the male gametophyte are initially separated from each other by distinct cell walls often traversed by plasmodesmata. Mature pollen grains have appreciable reserves of protein, lipid and starch. Results of histochemical and scanning electron microscopical observations are also reported and discussed.

The ultrastructure and ontogeny of pollen in Helleborus foetidus L. I. The development of the tapetum and Ubisch bodies.

ABSTRACT The ontogeny of the tapetum and Ubisch bodies in Helleborus foetidus L. has been examined at the ultrastructural level, and their development has been closely linked with that of the sporo-genous cell and pollen grains. During development the tapetum passes through successive phases of synthesis, maturity and senescence, ending in complete dissolution. During the anabolic phase of growth, precursors of the Ubisch bodies are formed as spheroidal vesicles of medium electron density within the tapetal cytoplasm; they are associated with a zone of radiating ribosomes, which, as development proceeds, can clearly be seen to be situated on strands of endoplasmic reticulum. The callose special wall round the microspores and the tapetal cell wall now disintegrate and the pro-Ubisch bodies are extruded through the cell membrance of the tapetal cells, where they remain on the surface of the anther cavity and soon become irregularly coated with sporopollenin. Deposition of sporopollenin continues on the Ubisch bodies at the same time as upon the exines of the developing pollen grains. In both cases, the later stages of sporopollenin deposition are associated with electron-transparent layers of unit-membrane dimensions appearing in section as white lines of uniform thickness. Continuing deposition of sporopollenin leads to the formation of compound or aggregate Ubisch bodies. It is conjectured that the sporopollenin is synthesized from the compounds of low molecular weight released into the anther loculus by the breakdown of the callose special wall and the tapetal cell wall. The final stages of tapetal autolysis involve the disappearance of all the cell organelles. An attempt is made to relate the findings to those described in other recent studies on Ubisch body formation and to combine them in a common ontogenetic pattern.